1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a driving system for a backlight unit where a dimming signal is supplied from a system unit to an inverter unit, a liquid crystal display device including the driving system and a method of driving the liquid crystal display device.
2. Discussion of the Related Art
In general, liquid crystal display (LCD) device have advantages such as a light weight, a thin profile and a low power consumption and have been widely used for a notebook computer, an office automation apparatus and a audio/video machine. Specifically, active matrix liquid crystal display (AM-LCD) devices where a thin film transistor (TFT) is used as a switching element have advantages in displaying moving images.
FIG. 1 is a view showing a liquid crystal display device according to the related art. In FIG. 1, a liquid crystal display (LCD) device 10 includes a liquid crystal panel 20, a backlight unit 30, a control unit 40, an inverter unit 50 and a system unit 60. The backlight unit 30 supplies light to the liquid crystal panel 20, and the control unit 40 supplies a control signal, a gate signal and a data signal to the liquid crystal panel 20. The inverter unit 50 controls a power supplied to the backlight unit 30, and the system unit 60 controls the control unit 40 and the inverter unit 50.
Although not shown in FIG. 1, the liquid crystal panel 20 includes a plurality of pixel regions and displays images using the gate signal and the data signal. The backlight unit 30 includes a plurality of lamps for supplying light to the liquid crystal panel 20. The control unit 40 includes a printed circuit board (PCB) having a timing controller 42 and a driving integrated circuit (D-IC) thereon. The control unit 40 supplies a plurality of control signals and an RGB signal for displaying images to the liquid crystal panel 20. In addition, the control unit 40 receives a dimming signal for controlling the backlight unit 30 from the system unit 60 and supplies the dimming signal to the inverter unit 50 with or without modulation. The inverter unit 50 controls emission of the backlight unit 30 using the dimming signal from the control unit 40. The system unit 60 supplies an image signal and a plurality of driving signals to the control unit 40 and supplies the dimming signal to the inverter unit 50. The system unit 60 includes an external interface circuit such as a television system and a graphic card.
In a cathode ray tube (CRT) of an impulsive type where an image is instantly displayed during a frame, deterioration seldom occurs in displaying a moving image. In an LCD device of a continuous type where an image is continuously displayed during a frame, the deterioration such as a motion blur and a tailing may occur in displaying a moving image because of a slow response property and a holding property of the liquid crystal. For example, the motion blur may refer to a blur of a moving object in an image and the tailing may refer to a border drag of an object in an image. The deterioration of the moving image in the LCD device may not be completely removed even when the response time of the liquid crystal is shorter than the single frame.
To improve the deterioration of the moving image in the LCD device, a scanning method of driving the backlight unit of the LCD device has been suggested.
FIGS. 2A and 2B are perspective views showing a scanning method of driving a backlight unit of a liquid crystal display device according to the related art, and FIG. 3 is a view showing emission control signals for a scanning method of driving a backlight unit of a liquid crystal display device according to the related art. In FIGS. 2A, 2B and 3, first to eighth lamps L1 to L8 are disposed under a liquid crystal panel 20, and the liquid crystal panel 20 includes first, second and third regions A1, A2 and A3 divided according to simultaneous on and off of the first to eighth lamps L1 to L8. In addition, the first and second regions A1 and A2 corresponding to upper and lower portions of the liquid crystal panel 20 is defined as a first block B1 where the first, second, seventh and eighth lamps L1, L2, L7 and L8 are simultaneously turned on and off, and the third region A3 corresponding to a middle portion of the liquid crystal panel 20 is defined as a second block B2 where the third, fourth, fifth and sixth lamps L3, L4, L5 and L6 are simultaneously turned on and off.
The first block B1 including the first, second, seventh and eighth lamps L1, L2, L7 and L8 and the second block B2 including the third, fourth, fifth and sixth lamps L3, L4, L5 and L6 are turned on and off at a timing different timing with each other. For example, the first, second, seventh and eighth lamps L1, L2, L7 and L8 of the first block B1 are turned off during a first half frame of a single frame and turned on during a second half frame of the single frame, while the third, fourth, fifth and sixth lamps L3, L4, L5 and L6 are turned on during a first period slightly prior to the first half frame of the single frame and turned off during a second period slightly prior to the second half frame of the single frame.
Accordingly, in the LCD device driven by a 2-block scanning method, only a middle portion of an image corresponding to the second block B2 is displayed during most of the first half frame of the single frame and no image is displayed during a last part of the first half frame of the single frame. In addition, only upper and lower portions of the image corresponding to the first block B1 are displayed during most of the second half frame of the single frame, and the whole image corresponding to the first and second blocks B1 and B2 is displayed during a last part of the second half frame of the single frame. Since only the middle portion of the image corresponding to the second block B2 is displayed during most of the first half frame of the single frame and only the upper and lower portions of the image corresponding to the first block B1 are displayed during most of the second half frame of the single frame, the image are displayed similarly to an impulsive type of the CRT. The LCD device driven by a scanning method may have a quasi-impulsive type. As a result, deterioration in display quality of a moving image such as a motion blur and a tailing is improved.
In an LCD device driven by a 2-block scanning method, since a plurality of lamps of a backlight unit are divided into two blocks and the two blocks including the plurality of lamps are turned on and off at different timings, two dimming signals for the two blocks are required. Accordingly, the system unit 60 transmits first and second dimming signals to the control unit 40, and the control unit 40 transmits the first and second dimming signals to the inverter unit 50. The inverter unit 50 adjusts lighting of the first, second, seventh and eighth lamps L1, L2, L7 and L8 using the first dimming signal and adjusts lighting of the third, fourth, fifth and sixth lamps L3, L4, L5 and L6 using the second dimming signal. The system unit 60, the control unit 40 and the inverter unit 50 may be defined as a driving system for a backlight unit 30.
FIG. 4 is a view showing a driving system for a backlight unit of a liquid crystal display device according to the related art. In FIG. 4, a system unit 60 includes first and second system connectors 60a and 60b, a control unit 40 includes first and second control connectors 40a and 40b, and an inverter unit 50 includes first and second inverter connectors 50a and 50b. The first system connector 60a of the system unit 60 is connected to the first inverter connector 50a of the inverter unit 50 through a first cable CB1, and the second system connector 60b of the system unit 60 is connected to the first control connector 40a of the control unit 40 through a second cable CB2. In addition, the second control connector 40b of the control unit 40 is connected to the second inverter connector 50b of the inverter unit 50 through a third cable CB3. The first, second and third cables CB1, CB2 and CB3 may include a flexible flat cable (FFC).
The system unit 60 transmits a driving power source signal, a lamp flash signal and a lamp status signal to the inverter unit 50 through the first system connector 60a, the first cable CB1 and the first inverter connector 50a. For example, each of the first system connector 60a, the first cable CB1 and the first inverter connector 50a may include 14 pins. A pin map for the 14 pins is illustrated in TABLE 1.
TABLE 1pin numbersymbolillustration of signal1~5VBLpower source voltage (+24 V) 6~10GNDground voltage11NCno connection12VON/OFFvoltage for turning on and off lamp (0 V~5 V)13NCno connection14STATUSlamp status
The system unit 60 transmits first and second dimming signals and an image signal to the control unit 40 through the second system connector 60b, the second cable CB2 and the first control connector 40a. In addition, the control unit 40 transmits the first and second dimming signals to the inverter unit 50 through the second control connector 40b, the third cable CB3 and the second inverter connector 50b. 
The control unit 40 includes a timing controller 42, and the first and second dimming signals received from the system unit 60 is transmitted to the inverter unit 50 without modulation or with modulation by the timing controller 42. Accordingly, the control unit 40 transmits the first and second dimming signals to the inverter unit 50 without modulation. Alternatively, the control unit 40 modulates the first and second dimming signals based on a result of analyzing the image signal by the timing controller 42 and transmits the modulated first and second dimming signals to the inverter unit 50. For example, each of the second control connector 40b, the third cable CB3 and the second connector 50b may include 4 pins. A pin map for the 4 pins is illustrated in TABLE 2.
TABLE 2pin numbersymbolillustration of signal1OPTIONoption2SCAN1first dimming signal3SCAN2second dimming signal4GN\Dground voltage
In a driving system for a backlight unit of an LCD device according to the related art, a plurality of signals including first and second dimming signals are transmitted through a plurality of connectors and a plurality of connectors and the backlight unit is driven by a 2-block scanning method, thereby deterioration in displaying a moving image improved. However, since a lot of connectors and cables are used in the driving system, the structure of the driving system becomes complicated and fabrication cost of the LCD device increases.